Depending on specific requirements, it is necessary in networks such as optical networks for certain component signals or channels of a WDM (wavelength-division multiplex) signal to be dropped in network nodes, i.e., supplied to local sides for further processing, and for other component signals or channels to be added to the WDM signal or looped through the node, amplified there if appropriate, and supplied to one or more additional network nodes as a WDM signal. For this purpose, the signal transmitting device of a network node is usually constructed in modular form since different circuitry components are used, depending on the concrete requirements in the network node in question.
For example, passive and active optical and/or electronic filter components, optical amplifiers and active channel modules or channel cards are used as modules in the realization of an optical network node.
Such modules, particularly channel cards, are necessary in a multitude of different designs in known signal transmitting devices, depending on the purpose for which they are used. They differ, for instance, in the properties of transceiver modules that are necessary for connecting the respective channel card to the local side of a network node, or to corresponding additional local-side signal processing devices or to corresponding additional remote-side signal processing devices of the network node or the entire additional network. The transceiver modules can be different, for example, regarding the coupling of the optical side to various optical waveguide types (single-mode fibers, multimode fibers), regarding the respective wavelength of the optical transmitting element and/or the optical receiving element that is being used, or regarding the data rate of the respective signal to be transmitted or received.
The structure of the channel cards can further differ in relation to the tasks to be undertaken by the card. For instance, it can be necessary merely to amplify and/or process the received signal and loop it through the network node, without dropping the respective channel in the network node. On the other hand, if a signal or channel is to be dropped, then a conversion of the signal from a received wavelength to another, local transmission wavelength and vice versa can be required. If the card is to realize a protection mechanism, then it is necessary to provide two transceiver units on the channel card on the remote side, wherein both transceiver modules can be controlled with the same transmission signal in the direction of the remote side of the channel card.
As already briefly indicated above, producing a corresponding channel card for each special application purpose and using it as a module in an entire signal transmitting device for the realization of a network node is already known. If the demands on the respective network node change, for instance, if different transmission wavelengths are to be used on the local side of the network node or the remote side of the network node for the respective channel or channels, then the channel card can be replaced by a different channel card.
For the user or the manufacturer of such signal transmitting devices there is therefore the disadvantage that a great number of different channel cards must be acquired or manufactured and kept in inventory. In addition to the fact that special channel cards must be developed for each application case, this leads to high costs for the individual channel cards.